Revitalization of Rivers in India Draft Policy - Isha Guru Jaggi Vasudev

Revitalization of Rivers In India
Draft Policy Recommendation
In this regard, a multitude of the methods have been developed which can be
conveniently categorized into four basic approaches as follow:
1. Graphical base flow separation
2. Filtering-algorithms
3. Frequency Analysis
4. Recession Analysis
The direct flow is primarily the direct response of a rainfall event and includes
the overland flow (runoff) and the lateral flow in the soil profile, also known as
interflow. The base flow is a component of streamflow which is discharged from
the natural storage of aquifers. Certain streamflows can be affected by both direct
flow and / or base flow components. Many streamflows can acquire modified base
flow situations due to the abstraction and use of water resource directly from the
stream or from the groundwater storage. A streamflow can also be affected by the
interruption of the direct flow such as by diversion of runoff and water harvesting
mechanisms. Therefore it is necessary to separate the direct and base flow of a
streamflow in order to understand the component that is more influential on
the stream flow as well as to identify the component which is more likely to be
affected by land use changes. Moreover in order to have a targeted policy in water
resource development and use, it is essential to have a responsible estimation of
the direct and base flow components of the stream flow.
The graphical methods separate the base flow on a discharge duration graph by
connecting an intersection point of base flow and direct flow upon the hydrograph
raising limb’s lowest flow point (at a point where direct flow is assumed zero) to
a point on the falling limb where it is assumed all flows are changed to base flow.
There are several methods that can be used to get the point where direct flow ends
upon the falling limb part of the hydrograph. The most popular one is an empirical
formula given by following equation (Linsley et al., 1975): D=0.827A 0.2
Where, D is the number of days between the storm crest and the end of the quick
or direct flow and A is the area of the catchment in square kilometers.
In stream flow separation, the most frequently used method is the filtering
separation method which separates base flow from the streamflow time series
294 Annexures